We propose to study the logical structure of a single binary decision during eukaryotic development. We will attempt to determine the factors controlling which of two developmental pathways the cells take. It is the spatial and quantitative regulation of these factors which determines the proportion and location of each cell type and hence the form of the mature organism. A suitable model for such a study can be found in the simple eukaryote Dictyostelium discoideum. During its development, a single precursor cell (the amoeba) gives rise to only two differentiated cell types (stalk cells and spores). We shall first define the two pathways by enzymatic markers or 2-D gel techniques using cell populations enriched for one or other developmental pathway. We shall use genetic techniques to demonstrate that the putative markers do indeed comprise parts of obligatory pathways leading to the formation of each cell type. In our study of the factors controlling the expession of the two pathways, we shal continue our work on the purification and characterization of an oligosaccharide-containing differentiation inducing factor (DIF) we have discovered. This factor induces stalk-cell differentiation but not spores and may be cell-type specific, i.e. a morphogen. We shall be able to study its pathway specificity once we have biochemically defined the two pathways. Immunological techniques will be used to study its cellular localization and spatial distribution in the developing organism.